The present invention is directed to creating in-mold and in-line decorated articles having higher quality than previously attainable, greater permanence than previously available, using molding techniques previously excluded, using processes and materials previously excluded, and offering improvements in yield, throughput and scrap rates. The present invention provides images of near photographic quality that are highly resistant to fading, chemicals and abrasion that can be produced using both thermoplastic and thermosetting processes. The present invention makes possible new in mold and in-line capabilities and provides new or improved opportunities for product decoration and for product labeling where permanence, long life, safety labeling, product identification, ownership or serialization labels, or production lot identification is needed.
Product manufacturers place a high value on the ability to deliver a product with a high quality graphic surface. This has traditionally required a trade-off between the quality of the image and the permanence of the image and its print media. The highest quality achievable has been to lithographically print adhesive labels, which are applied after aforesaid articles have been molded. These suffer from poor adhesion to many types of materials resulting in decorative labels that peel and degrade the appearance of the product. Loss of adhesion is exacerbated by environmental factors such as moisture and large changes in temperature and is particularly acute in outdoor applications. The loss of labels containing safety related information is obviously a much more serious issue. Labels on products used by small children also present a choke hazard should the labels come off. In many cases information is placed onto the article using other post-molding decorating techniques such as heat transfer and pad and screen printing. These techniques result in the lowest quality image and are generally limited to one or two colors in relatively non-complex designs. In many cases, an image such as a logo or lettering is actually a part of the mold creating a raised area that receives the transferred color. Both of these techniques also add complexity to the manufacturing process by adding a post-molding step wherein the article is given its graphic image. Not only do these techniques add cost and manufacturing cycle time, but aforesaid techniques also introduce opportunities to convert a part into a quality reject if the image application is not done perfectly. Neither adhesive labels nor post mold decorating techniques involving transfer of image or color can effectively decorate over compound curvature areas or the sides of raised areas. Current art is essentially limited to flat or single curvature surfaces.
The shortfalls inherent in aforesaid post molding decorating techniques have resulted in the development of in-mold decorating techniques. In-mold decorating is characterized by the preparation of graphics, normally using screen-printing techniques on a polymer film material of composition compatible with the polymer to be used in molding the part. The film traditionally used for said in mold decorating is clear allowing the underlying molded polymer to show through. Many techniques use complex multi-layered films in an attempt to achieve a satisfactory in-moldable product. The printed film is normally placed into the mold so that the molten polymer flows over the ink, which is trapped between said film and said polymer. Temperatures and pressures characteristic of said technique drives requirements for screen printing inks that can withstand said process. The graphic detail quality achievable by said techniques is limited by the environment in which said inks must remain stable and not wash out or flow with the molten polymer. The cost of screen printing, with the requirement to separately deposit each color, results in total costs that diminish the competitiveness of in-mold decorated products made using said technique.
There is a plurality of reasons why yields of good parts are lower than desired by manufacturers when using said in-mold decorating. Causative factors include damage to the graphic image on the surface of the sheet during placement or molding, damage to the sheet itself during molding and lack of stability of the printed sheet in the mold during molding. Said graphic image damage results primarily from the robustness of the inks and lack of protection of same from the temperatures and pressures common in said molding processes. Said sheet damage results primarily from stretching or penetration of said sheet during molding due to the pressures of molding and the flow of molten materials over the sheets to their edges. Said lack of stability involves the movement of said printed sheet within the mold due primarily to the flow of molten material over said sheet causing said sheet to slide with respect to the mold surface or to lift from said mold surface. Said sliding results from insufficient coefficient of friction between said sheet and said mold surface. Said lifting results from said sheet presenting too much cross section to the flowing molten material, particularly when the entry of said molten material is not within the boundaries of said graphic sheet and said molten material must impinge upon the vertical edge of said printed sheet. Said lifting problem is exacerbated by thicker printed sheets, which may be used to provide the needed tensile properties. Common techniques used to enhance said stability include inducing electrostatic charges between said sheet and said mold surface to prevent movement during molding, texturing said mold surface to increase friction between said sheet and said mold surface, and use of detents or pockets in the mold to constrain said printed sheet. Problems inherent in using said electrostatic charge techniques include the inability to maintain said charge at a high enough level and for a long enough period to properly complete the molding process. The dissipation of said charge is accelerated by the typical marginal dielectric characteristics of said printed sheet. Said surface texturing and use of detents or pockets are currently the best available options either used in lieu of or in concert with said electrostatic charging.
Some of the shortcomings of both post molding decorating and traditional in-mold decorating have been partially overcome in the area of thermoplastic compression molded products where a printed sheet has molten polymeric material fused to its non graphic surface. Compression molding using a billet approach falls into the category of a low stress technique thereby overcoming the problems inherent in highly tortuous techniques such as injection molding. U.S. Pat. No. 4,861,644 disclosed the printing using various techniques, including offset lithography, of microporous substrates. U.S. Pat. No. 4,892,779 discloses the fusion of a printed microporous sheet to other materials using a variety of molding techniques. Disclosed, but not claimed is injection and blow molding of polyolefins. U.S. Pat. Nos. 5,591,384, 5,626,339, 5,637,329, and U.S. Pat. No. 5,800,757 all disclose the manufacture of thermoplastic products with graphics molded into the surface of the product during manufacture using low stress molding techniques such as compression and structural foam molding. These patents cite the use of polymers which are compatible with the polymer used to make the sheet which is in-molded to said polymer. While U.S. Pat. No. 5,512,227 discloses use of polyolefin films and U.S. Pat. Nos. 4,418,033, 4,650,533, 5,227,222, 5,338,396, 5,514,427, 5,536,539, 5,698,283, 5,705,255, 5,707,472, and 5,795,527 disclose use of non-polyolefin films in injection molding applications, they demand a multi-layer “sandwich,” some involving adhesives to be an effective method of in-molding graphics during injection molding. Several of these techniques also require post-molding stripping of carrier sheets or layers from the finished part. Other patents, such as U.S. Pat. No. 5,676,981, require specialized techniques such as heating the graphic sheet to assure good adhesion and stability during the injection molding process. Other techniques such as described in U.S. Pat. Nos. 4,418,033 and 4,369,157 require a continuous strip of in-mold decorating material to be repeatedly advanced between each mold closure; this routinely introduces errors in alignment of the image to the part resulting in a quality reject. Still other techniques such as disclosed in U.S. Pat. Nos. 4,330,578 and 5,629,029 require specialized molds or double injection steps to accomplish the in-mold decorating operation. Still other techniques for blow molding such as disclosed in U.S. Pat. Nos. 4,808,366 and 4,983,348 do not result in actual permanent fusion attachment of the graphic image sheet to the finished part. Still other techniques such as disclosed in U.S. Pat. No. 4,427,615 require pins in the mold upon which to hang the printed sheet to be in-molded.
In summary, existing methods of achieving said in-molded graphics generally depend on the similarity of materials between the graphically printed film and the substrate material to which the graphic is molded. Said methods address only thermoplastic applications. Where the use of dissimilar materials is disclosed there are complex techniques, such as multi-layering, required to affect the molding. The current state of the art offers no techniques for in-mold decorating with lithographically printed images using high stress manufacturing techniques such as injection molding. Since the majority of current molding is injection, there is a need for a method of economically achieving high yield, high throughput in-mold decorating manufacture of high quality graphic products. The current state of the art offers no techniques for introduction of a three dimensional graphic into the cavity of a mold to produce a dimensional part decorated in the mold with graphics on all top and side surfaces. Since most polymeric materials undergo shrinkage during post-molding cooling, there are issues with in-mold decorating techniques not matching the shrink rate; the current state of the art does not offer techniques for in-mold decorating where the image will automatically exhibit the same shrink rate as the polymer into which it is molded.